There is a wide-area intranet-to-intranet communication system, in which intranets compatible with a plurality of bases distributed and arranged through a wide area on the basis of countries or regions are connected by a relay transfer medium including at least one of a relay line and a relay network to perform communication. Leakage of communication data to the outside needs to be prevented in the wide-area intranet-to-intranet communication system.
The following is a related art to the invention.
[Patent document 1] Japanese Patent Laid-Open Publication No. JP H10-271167